There is a significant need for more non-invasive monitoring of analytes in a patient. A particular disorder requiring such monitoring is diabetes mellitus, a disease that requires constant vigilance with respect to monitoring of the glucose levels of the subject. One approach to the non-invasive monitoring of blood glucose levels is to monitor glucose concentrations in tear fluid. While several methods for sensing glucose in tear fluid have been proposed, controversy remains as to the precise concentrations of tear glucose in normal and diabetic subjects and as to whether tear fluid glucose concentrations correlate with blood glucose concentrations.
The method of fluid collection has a significant impact on the level of accuracy and sensitivity of the glucose concentration measurement. Studies that involve mechanical irritation of the conjunctiva during sampling measure the highest tear glucose concentrations, while studies that avoid tear stimulation measure the lowest concentrations. Attempts to monitor tear glucose concentration in situ by using contact lens based sensing devices also are available but these contact lenses require calibration, lead to irritation after prolonged use, and are not truly “non-invasive”. Overall, the prior art methods have taught various devices and have shown the importance of the sampling method in determining tear glucose concentrations.
The present invention addresses a need for a safe, fast, non-invasive, and non-irritating method and device for the collection and sampling of tears.